Multivalent glycocalixarenes for lectin inhibition

Abstract

The growing knowledge of the biological role played by the glycoside cluster effect prompted us to design and synthesize compounds able to inhibit target lectins with high selectivity and efficiency by combining a multivalent presentation of ligands with carbohydrates tailored for the best-possible contact complementarity with the proteins. To this aim calixarenes were chosen as multivalent scaffolds because they offer the unique opportunity to easily change the valency, the molecular shape, the conformation and the symmetry of the glycocluster. The work reported in this Ph.D. thesis concerns the synthesis and properties of a series of calix[n]arenes containing units of galactose, lactose, LacNAc or LacNAc modified at 2-N or 3’ positions and connected to the macrocyclic structure via thioureido or triazole groups. These compounds showed high affinity for different types of galectins. Quite interestingly, the selectivity for the different lectins was confirmed to be also dependent on the calixarene conformation, pointing out the importance of the multivalent presentation in space of the glycosyl units. Enzymatic galactosylation and 2,3- and 2,6-sialylation reactions were also explored using glycosylcalixarenes as substrate. Moreover, NMR and computational studies were performed on selected glycocalixarenes in order to better understand the nature of the carbohydrate-lectin interactions in solution on an atomic level. At last, pentavalent glycocalix[5]arenes functionalized with carbohydrates of increasing complexity, including GM2 and GM1 oligosaccharides, were synthesized to allow a perfect match in valency with the target lectin, the pentavalent B subunit of cholera toxin. Preliminary ELISA tests remarkably showed an IC50 value in low nanomolar range indicating the GM1-derivatized glycocalix[5]arene to be one of the most efficient cholera toxin inhibitors known so far.